Sprinklers have long been used in automatic fire extinguishing systems in order to controllably disburse a fluid to suppress or extinguish a fire in a designated area. Typically, the fluid utilized in automatic fire extinguishing systems is water, however systems have also been developed to disburse other fire extinguishing fluids. In one common design, sprinklers include a solid metal base with an inlet connected to a pressurized supply of water or other fire extinguishing fluid, and a deflector which alters the trajectory of the water in an optimum pattern when discharged from the base outlet orifice. In many conventional sprinklers the deflector is fixedly spaced from the outlet by a pair of rigid arms and mounted on a boss joining the arms. A trigger element is positioned between the deflector boss and the outlet orifice closure seal.
In another common recessed, pendant version of the sprinkler, the deflector is movable and stored proximate to the base. A housing extends around the deflector and sprinkler body and forms a recess up into the ceiling in which the sprinkler is located. A fluid seal, also positioned within the interior of the sprinkler, is maintained in the closed position by a pair of levers or actuators depending below the bottom of the sprinkler body. The levers are held in an inwardly biased or closed position by a trigger mechanism which is thermally responsive in the temperature range indicative of a fire. The trigger mechanism is commonly a thermally sensitive fusible link. Thus, under normal temperatures, the presence of the thermally sensitive fusible link prohibits fluid flow from the sprinkler. When the temperature within the designated area rises to a preselected value due to a fire, the fusible link separates, causing the levers to move in an outward direction and thus permits downward movement of the deflector plate from the interior of the sprinkler to a preselected distance within the interior of the designated area. The separation of the fusible link also opens the fluid seal, thereby enabling pressurized water to travel through the sprinkler and into the designated area in order to suppress or extinguish a fire.
The prior art has advanced fusible link trigger mechanisms which also function to conceal the bottom outlet of the sprinkler. For example, U.S. Pat. No. 4,596,289 issued to Johnson discloses a combined trigger element and concealing mechanism having two complementary strut retaining members which maintain the fluid seal in a closed position. The outer surfaces of these strut retaining members are joined by a heat fusible material which is covered by a heat conductive cover. In this design, the bottom outlet of the sprinkler is entirely enclosed by the combined trigger and concealing mechanism. In a similar design, U.S. Pat. No. 3,783,947 issued to Dix et al. advances a combined cover and trigger mechanism having a cover member which completely encloses the open portion of the bottom of the sprinkler. The cover member is attached to a lever in operational contact with a strut. This strut maintains a fluid seal in the closed position under normal temperatures. The cover member is attached to the interior surface of the sprinkler body by a heat fusible tab. When this heat fusible tab is exposed to a preselected temperature, its thermal degradation causes the release of the cover member which in turn imparts movement of the lever mechanism, and hence actuates the strut to thereby open the fluid seal.
In both of these designs, the cover mechanism entirely encloses the bottom of the sprinkler, with the heat fusible material being located on the interior surface of the cover. When the temperature is elevated due to the presence of a fire in the designated area, the thermal energy issued from the fire is constrained to pass in an upward direction from the outer surface of the cover member towards the heat sensitive compound. Since the cover member completely encloses the bottom region of the sprinkler, the inner surface of the cover member and the heat sensitive agent remains at ambient or near ambient conditions until thermal energy penetrates the cover member and reaches the heat sensitive agent. As a consequence of the prior art combined trigger and concealing mechanisms, the responsiveness of the sprinkler to which they are attached is often reduced. That is, when a fire occurs in the designated area, the temperature of the room may be at the preselected temperature at which the sprinkler is to be actuated. However, because conduction is forced to occur in only one direction, there is a time gap between the achievement of a particular room temperature and the actuation of the sprinkler. Delayed actuation of a sprinkler in the presence of a fire is unacceptable because such delay may provide a sufficient time period for which the fire to spread outside of the designated area.
Consequently, there exists a need for a responsive and reliable combined trigger and concealing device which overcomes the difficulties encountered by the prior art.